El Ni(?)o Change Under 1.5 And 2.0? Global Warming Above Pre-industrial And Its Possible Impact On Summer Precipitation Over China

By using simulation results of the Community Earth System Model(CESM)under the global warming of 1.5?/2.0?(relative to the pre-industrial)and its 20th century historical simulation results,we study the amplitude,period and frequency of El Nino under the global warming of 1.5?/2.0?,also the responses of the tropical atmosphere are researched.Lastly,we discuss the possible impacts of two types of El Nino on summer precipitation over China under the global warming.The main conclusions are as follows:(1)Under the global warming of 1.5?/2.0?,the responses of the El Nino key areas to warming are different,showing a trend of increasing temperature from west to east.Global warming has no significant effect on the ENSO cycle,but the amplitude increases significantly,and there is an eastward expansion trend.In the observation and present day(1976-2005),the frequency of extreme and moderate events is equal,and the frequency of extreme events in 1.5 ? scenario is 1.5 times than the present day,and the frequency of extreme events in 2?scenario is 2.3 times than the present day.The increase of temperature will lead to an increase in the frequency of extreme events,the frequency of extreme events increases nonlinearly,the increase of 0.5? leads to a faster occurrence in extreme events,but the sum of extreme and moderate events in 1.5? and 2? scenarios is equivalent to the present day.(2)Under the global warming of 1.5?/2.0?,the pressure gradients of tropical pacific are decreased from east to west,the lower zonal east winds of the equatorial middle-east Pacific are weakened and the westerly anomaly are enhanced,the updraft flow and the equatorial precipitation are both increased as well,the Walker circulation weakens.The change of Walker circulation intensity is related to global warming,but the central position is basically unchanged,the main change is the updraft flow of the lower winds,the variation of each factor which appears at 2.0? is stronger than that in 1.5?.The upstroke of Walker circulation corresponding to the central El Nino events is stronger than the eastern El Nino events,while the eastern El Nino events correspond to a wider range of Walker circulation.The central position of each circulation system has no significant change in present day and 1.5?/2?scenarios,but the intensity changes greatly,the influences of the central and eastern El Nino events to circulation systems are asymmetric in intensity and space.(3)The East Asian Hadley circulation and the summer precipitation over China corresponding to two types of El Nino events are sigrnificantly changed under the global warming of 1.5?/2.0?.The rising motion of the East Asian Hadley circulation is strengthened in 1.5?/2? scenarios,the increase of 0.5? leads to a significant increase of updraft flow.In 2? scenario,the summer precipitation over China in next year corresponding to eastern El Nino events has changed,the intensity of the summer Hadley circulation over China in next year corresponding to central El Nino events is stronger than that of eastern El Nino events,also the precipitation anomaly is more than that of the eastern El Nino events.The combination of Philippines anticyclone and different circulation systems in the northwest Pacific in 850 hPa affects the water vapor transport of the bay of Bengal and the northwest Pacific to the east regions of China,and further influences the summer precipitation over China in present day and 1.5?/2? scenarios.The water vapor transport channel in northwest and northeast China is controlled by teleconnection type,water vapor mainly comes from high latitude regions such as the Arctic Ocean.At the same time,the geopotential height of 500 hPa can impact the rain band of Yangtze river basin,which can also cause the shift of rain band and precipitation anomaly.